PHALLUS MORPHOLOGY IN CAECILIANS 



153 



in caecilian systematics. There is evidence of considerable ontoge- 

 netic variation in the development of blind sacs and phallodeal 

 ornamentation, emphasising the need for systematic comparisons to 

 be of co-ordinate developmental stages or of developmental trajec- 

 tories. There is also evidence of variation in adults in the sizes of the 

 urodeum and phallodeum, and the exact form of ridges, their orna- 

 mentation, and other phallodeal structures, at least some of which is 

 seemingly correlated with breeding cycles. Despite Wake's (1998: 

 183) statement that the morphology of the phallodeum of 

 Scolecomorphus 'is indeed consistent within the species', the same 

 paper clearly documents intraspecific variation in the number of 

 phallodeal spines in Scolecomorphus uluguruensis and S. villains 

 (Boulenger, 1895). Functional considerations lead us to speculate 

 that additional intraspecific variation in phallodeal ornamentation 

 occurs because the phallodeum serves both reproductive and excre- 

 tory roles. In individuals with well-developed tuberosities, these can 

 interdigitate in situ to seemingly obstruct the cloacal lumen. We 

 hypothesise that in these species, at least, cloacal ornamentation 

 would be elaborated at times of courtship but reduced at other times. 

 If correct, differences in reproductive condition would need to be 

 taken into account in any systematic comparisons. 



Our observations suggest that the pattern of major longitudinal 

 ridges and often also the number and position of phallodeal tuberosi- 

 ties or other ornamentation is mostly constant within species. The 

 same general pattern occurs in 1 1 specimens of Hypogeophis 

 rostratus, the largest sample of a single species that we have 

 examined in detail. However, detailed study of ontogenetic and 

 population variation is needed to test this constancy and to deter- 

 mine whether variations in the form of phallodeal ornamentation are 

 of systematic utility. Thus, future studies should attempt to increase 

 sample sizes for at least some species. Of the 33 species examined by 

 Wake (1972), her largest sample was 29 specimens of Gymnopis 

 proximo (Cope, 1877) whereas sample sizes for the remaining 

 species were low (mean = 1.7), providing little basis for assessing 

 variation. Wake ( 1 972) did not discuss intraspecific variation in any 

 species. 



Closely related species (e.g. congeners) tend to have similar 

 cloacal morphologies, providing a strong indication that the cloaca 

 will be a source of stable phylogenetic characters. For example, the 

 absence of a definitive colliculus or any other obvious division of the 

 cloaca into urodeal and phallodeal chambers is a very striking 

 putative synapomorphy of Dermophis and Gymnopis. These genera 

 have been considered closely related (e.g. Nussbaum & Wilkinson. 

 1989) but there are no previously reported uniquely derived 

 characters. Similarly, the general form of the longitudinal phallodeal 

 ridges and their ornamentation in Schistometopum thomense and S. 

 gregorii appears to offer the first known unique diagnostic character 

 for Schistometopum. On the other hand, congeners can sometimes 

 be readily distinguished by clear-cut, discrete differences in the 

 patterns of phallodeal ridges and topological relations in their 

 ornamentation. 



Contrary to Wake (1972), our investigations of Uraeotyphlus 

 suggest that, in at least some cases, cloacal morphology may not be 

 species specific. Instead, it appears that some species that can be 

 clearly differentiated based on traditional morphological characters 

 have a common pattern of phallodeal ridges and ornamentation. 

 Species specific differences in these examples may yet be found in 

 the details of the form of phallodeal morphology, but additional 

 work is needed to test this. 



In this survey we have concentrated upon the gross structural 

 features of the caecilian cloaca. The lumenal surface of the cloaca 

 appears to be also covered in many minor ridges and grooves 

 (striae). This micro-ornamentation may also yield useful systematic 



data but, as with more macroscopic features, studies of this must 

 take into account potential intraspecific variation. In some cases, 

 where we have described major structures as terminating, it might be 

 more accurate to describe them as giving rise to, or being supplanted 

 by, striae. For example, in Hypogeophis rostratus, where the main 

 dorsolateral longitudinal ridges and their sulci 'terminate' anteriorly, 

 close to the colliculus, they more accurately continue into incon- 

 spicuous striae (MW, pers. obs.). These bend around the lateral 

 margins of the colliculus and open into channels running alongside 

 the main mid-dorsal urodeal ridge. We suspect this arrangement 

 constitutes the passage through which sperm travel from the urodeum 

 to the phallodeum, to be delivered to the female via the dorsolateral 

 sulci that are such a prominent feature of the phallus. 



Acknowledgements. It is a pleasure to thank our esteemed colleague 

 and friend Garth Underwood for inspiring our research and for enlightening 

 discussions of systematics, cloacae and histology. The assistance in provision 

 of material of too many people to name individually has been indispensable 

 to this work, and is gratefully acknowledged. Thanks to Christian Klug and 

 Claudine Levasseur for assistance with translations, Alex Kupfer for helpful 

 discussions of cloacal form and function, and Harry Taylor for Fig. 10. MW 

 is grateful to Ron Nussbaum for fostering and encouraging his interest in 

 caecilian cloacae, and to David Sever for helpful discussion of amphibian 

 urogenital systems. This paper was improved by critiques from Barry Clarke. 

 Alex Kupfer, Simon Loader and Hendrik Miiller and supported in part by 

 NERC "rants GST/02/832 and GR/9/2881. and an MRF award. 



REFERENCES 



Bons, J. 1986. Donnees histologiques sur le tube digestif de Typhlonectes 



compressicaudus (Dumeril et Bibron. 1841) (amphibien apode). Memoires de la 



Sociele Zoologique de France 43: 87-90. 

 Duellman. W. E. & Trueb, L. 198ft. Biology of amphibians. New York, 670pp. 

 Duvernoy, G. L. 1849. Cours d'histoire naturelle des corns organises professe au 



college de France. Revue et magasin de Zoologie 1849: 179-189. 

 Exbrayat, J-M. 1991. Anatomie du cloaque chez quelques gymnophiones. Bulletin de 



la Soncie Herpetologique de Frame 58: 31-43. 

 1996. Croissanceet cycle du cloaque chez Typhlonectes compressicaudus (Dumeril 



et Bibron. 1 84 1 ). amphibien gymnophione. Bulletin de la Sociele Herpetologique de 



trance 121: 93-98 

 Gower, D. J., Kupfer, A., Oommen, O. V., Himstedt, W., Nussbaum, R. A., Loader, 



S. P., Presswell, B., Miiller, H., Krishna, S. B., Boistel, R. & Wilkinson, M. 2002. 



A molecular phylogeny of ichthyophiid caecilians (Amphibia: Gymnophiona: 



Ichthyophiidae): Out of India or out of southeast Asia? Procceedings of the Royal 



Society B 269: 1563-1569. 

 Giinther, A. C. L. G. 1864. Reptiles oj British India. London. 452pp. 

 Hedges, S. B., Nussbaum, R. A., & Maxson, L. R. 1993. Caecilian phylogeny and 



biogeography inferred from mitochondrial DNA sequences of the I2S rRNA and 



16S rRNA genes (Amphibia: Gymnophiona). Herpetological Monagaphs 7: 64-76. 

 Himstedt, W. 1996. Die Blindwiihlen. Magdeburg, 160pp. 

 Largen, M. J., Morris, P. A. & Yalden, D. W. 1972. Observations on the caecilian 



Geotrypetes grandisonae Taylor (Amphibia: Gymnophiona) from Ethiopia. Monitore 



Zoologico Italiano, Supplemento IV 8: 185-205. 

 Noble, G. K. 1931. The biology of the Amphibia. New York, 577pp. 

 Nussbaum, R. A. 1977. Rhinatrematidae: a new family of caecilians (Amphibia: 



Gymnophiona). Occasional Papers of the Museum of Zoology, University of Michi- 

 gan 682: 1-30. 



1985. Systematics of Caecilians (Amphibia: Gymnophiona) of the family 



Scolecomorphidae. Occasional Papers of the Museum of Zoology. University of 

 Michigan 713: 1-19. 



& Pfrender, M. E. 1 998. Revision of the African caecilian genus Schistometopum 



Parker (Amphibia: Gymnophiona: Caeciliidae). Miscellaneous Publications, Mu- 

 seum of Zoology, University of Michigan 187: 1-32. 



& Wilkinson, M. 1989. On the classification and phylogeny of caecilians 



(Amphibia: Gymnophiona). a critical review. Herpetological Monogaphs 3: 1-42. 



Pillai. R. S. & Ravichandran, M. S. 1999. Gymnophiona (Amphibia) of India: a 

 taxonomic study. Records of the Zoological Survey of India, Occasional Paper 172: 

 1-117 



